1. Field of the Invention
The present invention relates to a ball grid array integrated circuit package.
2. Description of Related Art
Integrated circuits are typically housed within a package that is soldered to a printed circuit board. One type of integrated circuit package is a ball grid array (BGA) package. BGA packages typically have a plurality of electrically conductive solder landings arranged in a two dimensional array along the bottom surface of the package. The solder landings are coupled to the integrated circuit by vias that extend through the body of the package.
Attached to each solder landing is a ball of solder that is subsequently reflowed when the package is mounted to the printed circuit board. The solder balls are typically attached to the package by placing hard solder balls on the solder landings and then reflowing the solder. The solder balls reharden as a sphere that is attached to the landings. To prevent the solder from flowing to an adjacent soldering landing and shorting the package, a solder mask is typically applied to the bottom package surface. The solder mask has a plurality of openings that are concentric with the solder landings and allow the solder balls to be attached to the package. To fully insure that the solder remains in the area of the solder landing, the openings in the solder mask typically have a diameter that is smaller than the diameter of the landings.
To improve the solder interface between the solder balls and the solder landings a solder flux is typically applied to the conductive package surfaces and cleaned after the balls are placed onto the landings. It is difficult to remove all of the solder flux from the solder mask openings. Consequently some flux remains within the openings when the solder balls are placed onto the package. It has been found that the remaining flux within the solder openings can degrade the solder joint of the solder balls.
Additionally, the tolerances of the solder mask openings are relatively large, resulting in openings of different sizes. The different size openings create solder balls with different heights. Any lack of coplanarity between the solder balls and the printed circuit board may produce a final assembly with less than robust solder joints. It would therefore be desirable to have a package and method for producing a BGA package which has a plurality of uniform and robust solder joints.